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West Seattle Weather Watch: Alki mudslide closes road

“Woke up to neighbor pounding on our door…landslide,” wrote a resident along 55th SW in Alki, where, as you see in our photo, the slide pushed a van across the road. 55th is closed at Alki SW as a result:

SDOT is out checking the slide scene – we’ll check with them later to see what the plan is. Here’s a closer look at the mud that came off the slope:

Neighbors are particularly concerned because they say sloping property in that area has been up for sale – we’re looking into that.

4 PM UPDATE: From SDOT’s Marybeth Turner: “SDOT is consulting with the Department of Planning and Development to determine who should clean up the slide.” Meantime, real-estate listings confirm that two parcels on that side of 55th are for sale, the one described as having “a relatively gentle slope” for $235,000, the other for $290,000; the listings say the site is in the process of being subdivided – though that is not evident in the DPD online records for the property. The zoning is for single-family housing.

33 Replies to "West Seattle Weather Watch: Alki mudslide closes road"

I think we’re dealing with a landslide issue, too. It’s hard for me to tell because it’s one house over, but it looks like trees are down right off of Jacobsen. It’s a spot that has seen some slide issues in the past and I think the lot is also for sale. WSB have you heard anything?

Spent alot of time on that hill side as a kid building tree houses and so on. It has always had slide and water run off issues. It was sub divided many years ago, and has been on and off the market since. There was a builder that started to do ground work on a couple of the parcels but the projects never materialized. Crazy the city would let someone build there. I almost bought the duplex across the street twenty five+ years ago, but with that hill slide,water issues and the thought of one building there kept me from doing so.

Please notice that the large stump / root ball and the other vegetation did NOT stop this slide, they just road with it. This is counter to what the City’s “experts” always put out at their Living With Landslides public meetings. They always put out that trees and foliage prevent landslides and it is just false. The roots of trees actually loosen the dense, stabil soils by a number of processes which take too much time to explain here.
2 of the 4 previous comments express concern about the possible sale of the property. They shouldn’t worry because the current rules will prevent anyone from building there. If the current owners want to do stablization work, they are are likely to be thwarted by DPD.
The reality is, if you want it to slide again, just let it revegetate and wait. It may take 20 to 50 years or more, but it will slide because that is the natural process. If you don’t want it to slide, allow someone like me to stabilize it and build on it. Require stabilzation to be done correctly then build on it and then plant your trees when they will have a chance to stay around.

Les, good deep-rooted vegetation does stabilize soils, to a point. But it takes time for the roots to and vegetation to establish sufficiently to do so, especially as the slope gets steeper.

With respect to the roots and the tree in the photo, it looks like a root ball from a dead/dying tree? Rotting roots from dead trees most certainly do not help with stabilization, and may contribute to the destabilization where there is not as much to help hold it in, as looks to be the case here.

Kate – where on Jacobsen are you talking about? I didn’t notice any slide issues on my walk there today.
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Re unstable slopes, really all of Seattle is uncompacted, unstable soils. Construction, trees, groundcover can all make a slope more stable, or less stable, depending.

From my 30+ years of cleaning up and rebuilding slopes that have failed, and from recognizing what I see in the world. I gained my knowledge under the tutorage of one of the pioneering soils engineers in the Northwest. We had numerous discussions about the processes of landslides.
I would be happy to discuss it with you but this isn’t a good format.

Mark, I’m willing to explain it to you too, and others as well if we get a place to do it. It’s really quite simple and obvious when you get the correct info, and if you are open to other opinions.
Mike you are right. There have been slides for a long while and they will continue, because nature wants it to be flat. However, we can increase the time between occurances by a factor of ten or more given proper drainage, grading and strucural retainage, especially if occasional maintainance is done.

Hey Les,
… deje vu my friend. Anyone that wants to see Les, Bernie and the crews handiwork, should drive by 5940 Beach Dr. S.W. and the residences on either side, they are testament of there skill and expertise. I can tell you from first hand experience, he knows that, of what he speaks, and is highly regarded by those familiar with building difficult sights.
Give our best regards to everyone.

What effect does shrubbery (low plants, unlikely to be caught by wind) rather than big trees have on slopes? To me, it seems logical that to stablilize a slope you’d want something not too tall and heavy, not likely to “tip, ” but with lots of root structure. I know blackerry bushes are a menace in other ways, but that’s why I made that comment.

But this is just my gut speaking. I’m interested to know what the different theories are (unless it will cause a huge angry debate here).

My experience is that Himalayan blackberry’s have very little root structure just the “Brain”. Most experts agree that the best retaining is a mix of native trees and shrubs. Western Red cedar is a favorite tree of mine. But its true that slides are part of the natural process.

Very glad to see Les Treal contributing to this discussion. Keep an open mind as he has years and years of field experience and knowledge.
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My Dad was a Geologist, and would always tell us kids that soils around here are lake layers in a cake, but they don’t stick together very well. Add a lot of weight, as in rainfall, or yes, even trees, and the top layer of the cake goes slip sliding away. Keeping the water out of the slope or controling it’s movement through the slope and decreasing the deadload on the uppermost layer of soil will reduce the chances of the area sliding.

Once again, here’s my post about trees and mudslides http://www.whereiamnow.net/2010/02/trees-and-mudslides.html A lot of what we used to believe about plants and mudslides has turned out to be wrong. Trees do not necessarily prevent mudslides. Nor do trees have “taproots” as was believed in the past.

Les-spot on. As someone who grew up on the street, the whole side of the street where the mudslide happened used to be full of blackberry’s. In the summer people would come and pick them to make Jelly or pie. They have been gotten rid of and now look what happened.

Hi Happiness- If you’re walking down Jacobsen, towards the water, the slide appears to have happened around the second crosswalk to the left of the guardrail. Earlier this fall I saw goats chewing their way through the bramble in that area too. Let me know what you think next time you walk by.

Kate – that spot – right next to the goats – has a well-underway construction project down below, with a newish retaining wall above the construction. Peeking over the edge, it looks like quite a bit of bramble was probably removed while they constructed the reatng wall, or maybe later to monitor whether the retaining wall was doing its job.
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Nothing has changed since yesterday, except the van owner has moved the van. The road is still closed and full of mud with the tree in the middle of the road. To me it actually looks like more mud has slipped down. Are they waiting for the slope to stabilize? When do they think that will be?

I also understand that the city wants to see whether the landowner is responsible for the cleanup or not – so maybe that’s the issue.

Regardless – how many days will the mud and tree sit there before the city deals w/ it?

Landslides are a natural process, but human interaction has acerbated the problem more than Mother Nature. Trees are very important in stabilizing a hillside, not only the roots, but also the leaf litter from deciduous trees. Dead leaves on the ground create a natural protective layer, repelling rainfall and keeping it from soaking into the soil. When too many trees are cut down for development or someone wants a better view, then the ground becomes saturated with water and mass wasting (landslides) can result.